CN1612505A - Apparatus and method for monitoring optical signal - Google Patents

Abstract

An apparatus and method for monitoring an optical signal are provided. In the apparatus, a polarization adjusting unit converts the state of polarization of an optical signal. A polarization beam splitter splits the optical signal into a first polarization component and a second polarization component perpendicular to each other. An optical intensity measuring unit measures the optical intensity of the first polarization component. A feedback control unit controls the polarization adjusting unit so that the first and second polarization components are aligned to the two axes of the polarization beam splitter. A scrambler scrambles the optical signal input to the transmission optical fiber. According to the apparatus and method, optical signal-to-noise ratio (OSNR) can be measured accurately.

Description

The apparatus and method of monitoring light signals

Technical field

The present invention relates to a kind of apparatus and method that in a wavelength division multiplexing (WDM) optical transmission system, monitor a light signal, more particularly, the present invention relates to a kind ofly not consider that at one polarization mode scatters the apparatus and method that accurately monitor a light signal in the optical transmission system of (PMD:polarazation mode dispersion).

Background technology

In a WDM optical transmission system, various image intensifers compensate light signal for the loss that is occurred in the optical transmission part, but the amplification that is produced in the amplifier simultaneously spontaneous emission (ASE) noise effect light signal.The ASE noise has reduced Optical Signal To Noise Ratio (OSNR), thereby has reduced the performance of system.Therefore, in order to monitor and evaluate the performance of WDM optical transmission system, need measure OSNR.

One wherein multipath conversion and the transmission a plurality of wavelength channels the WDM optical transmission system that can dynamically reconfigure in, OSNR may be different in each passage, because propagate along different routes from light signal that different node transmitted, and by way of the amplifier of varying number.Therefore, the ASE noise level may be different in each passage, thereby, in order accurately to evaluate the performance of each optical channel in the wdm system, need the OSNR of every passage be monitored.

In measuring the prior art of OSNR, be published in the article " A High-performance Optical Spectrum Monitor with High-speedMeasuring Time for WDM Optical Networks (for the high-performance spectrum monitor with high speed Measuring Time of WDM optical-fiber network) " of the people such as K.Otsuka among the scholarly publication 97 EuropeanConference on Optical Communication (97 ECOC Eeuropean Conference on Optical Communications) and disclose a kind of technology.Disclosed technology has been used a diffraction grating and a photodetector array in this piece article, spatially cutting apart each wavelength, and measuring light power, but also measure OSNR by this practice.The shortcoming of this technology is if suppose that the power of the light signal in each signal is constant, even then work as the ASE noise level difference of each passage in the WDM network that can dynamically reconfigure, also can measure an identical OSNR value in each passage.In addition, this technology is very responsive to light spacial alignment adjustment (alignment).

The another kind of prior art of measuring OSNR is, goes up article " disclosed a kind of technology among the Optical Performance Monitor BuildInto EDFA Repeater for WDM Networks (being built in the optical performance monitor in the EDFA transponder of WDM network) of the people such as K.Asahi that announce in " 98 Optical Fiber Conference (98 optical fiber meeting) ".This technology has been used an acousto-optic variable filter, scanning each wavelength, and measuring light signal power and ASE power, but also calculate OSNR by this practice.Yet this technology has a such shortcoming: can not accurately measure OSNR different in each passage.

The another kind of prior art of measuring OSNR is: the sequence number of people such as Y.C.Chung application is 6433864, disclosed technology in the United States Patent (USP) of " Apparatus for Monitoring Optical Signal-to-Noise Ratio ofOptical Signals in WDM Optical Transmission System (being used for monitoring the device of WDM optical transmission system light signal Optical Signal To Noise Ratio) " by name.The power of the light signal that a kind of basis of this technical proposal is measured by beat (beat) noise that utilizes electrical filter and detect with according to the light signal of multiplexed through separating (demultiplexing) calculates the method for OSNR, this method can be measured OSNR different in each passage, but may cause error because of the influence of undesirable signal, under the situation of measuring beat noise, may produce this undesirable signal with a predetermined frequency.In addition, the influence of polarization mode distribution (PMD) also may cause error.

Another kind of prior art is, people's such as J.H.Lee the disclosed technology of article " OSNR Monitoring Technique Using Polarization-Nulling Method (using polarization to balance out the OSNR surveillance technology of method) " in scholarly publication IEEE Photonics Technology Letters 2001 the 13rd volume.This method is used a quarter-wave plate and a linear polarizer, to adjust the polarization of light signal, and when polarizer and signal polarization are in level, calculate OSNR according to measured power output, and when they are in plumbness, when being the signal polarization disappearance,, calculate OSNR according to measured power output.Yet when PMD was present in the Transmission Fibers, light signal had two orthogonal polarization components that postpone mutually in time, i.e. two of polarization major states.Therefore, even adjusted signal polarization, polarizer can not make signal polarization balance out.Therefore, this technology has such shortcoming: when PMD increased, the error in the measured OSNR value increased.

Summary of the invention

The invention provides a kind of apparatus and method that accurately monitor the Optical Signal To Noise Ratio (OSNR) in each passage in a wavelength division multiplexing that can dynamically reconfigure (WDM) optical transmission system that are used in, wherein, the relative passage of ASE noise level and changing, and have the influence of polarization mode being scattered (PMD).

According to an aspect of the present invention, provide a kind of device that is used for monitoring light signals, this device comprises: a polarization adjustment unit is used to change a polarization state by the light signal that Transmission Fibers received; A polarization beam splitter, it will become mutually perpendicular first polarized component and second polarized component from the separate optical signals that the polarization adjustment unit is exported; A luminous intensity measurement unit is used to measure the luminous intensity of first polarized component; A feedback control unit, it is by using the signal of telecommunication frequency spectrum (electric spectrum) of second polarized component, and control polarization adjustment unit is so that can make two axles of first and second polarized components and polarization beam splitter align; And a scrambler (scrambler), if feedback control unit aligns two axles of first and second polarized components and polarization beam splitter, then this scrambler carries out scrambling to the light signal that is input to Transmission Fibers.

According to another aspect of the present invention, provide a kind of method that is used for monitoring light signals, this method comprises: conversion is by the state of the polarization of the light signal that Transmission Fibers received; The separate optical signals that polarized component has wherein been changed becomes mutually perpendicular first polarized component and second polarized component; Measure the luminous intensity of first polarized component; By using the signal of telecommunication frequency spectrum of second polarized component, carry out FEEDBACK CONTROL, so that can aim at adjustment, make it to align with two predetermined axles to first and second polarized components; And if by FEEDBACK CONTROL first and second polarized components and this two axles are aligned, then the light signal that is input to Transmission Fibers is carried out scrambling.

By this practice, one wherein the ASE noise level change with passage and exist in the WDM optical transmission system that can dynamically reconfigure of PMD influence, can accurately measure the OSNR of each passage.

Description of drawings

By the detailed description of reference accompanying drawing to the preferred embodiment of the present invention, above purpose of the present invention and advantage will become more apparent, wherein:

Fig. 1 be one according to the structure chart that is used for the device of monitoring light signals of the present invention;

Fig. 2 is expression simulation about the curve chart of the variable power of the major state (PSP) of polarization and the angle between the polarization beam splitter (PBS);

Fig. 3 is the structural representation of an experimental provision, and this experimental provision is used for testing according to the present invention a device that is used for monitoring light signals;

Fig. 4 is the OSNR measurement error value of prior art relatively and curve chart according to OSNR measurement error value of the present invention;

Fig. 5 is comparison for the OSNR measurement error value of the prior art of differential group delay (DGD:differential group delay) and curve chart according to OSNR measurement error value of the present invention; And

Fig. 6 is a flow chart of the performed step of the method that is used for monitoring light signals according to the present invention.

Embodiment

With reference to Fig. 1, Fig. 1 shows according to a kind of device that is used for monitoring light signals of the present invention, comprises a scrambler 110, light assembled unit 125, polarization adjustment unit 130, polarization beam splitter 135, a feedback control unit 136 and a luminous intensity measurement unit 160.Feedback control unit 136 comprises an optical detecting unit 140, filter cell 145, a power detecting unit 150 and a main control unit 155.OSNR monitoring arrangement according to the present invention is connected in a WDM optical transmission system, this optical transmission system comprise a transmission unit 105, multipath conversion unit 107, Transmission Fibers 115, one separate multiplexed (demultiplexing) unit 120 and a receiving element 165, and monitor OSNR.

Transmission unit 105 comprises a plurality of transmission units, a light signal in each transmission unit 105 output multichannel.The 107 pairs of multichannel light signals from transmission unit 105 outputs in multipath conversion unit carry out multipath conversion, and they are input to Transmission Fibers 115.Because the polarization mode that is present in the Transmission Fibers 115 scatters (PMD), experience mutually perpendicular two polarized components through the light signal of multipath conversion, promptly a time delay between the major state of two polarizations (PSP) is poor.

Separate multiplexed unit 120 and separate the multiplexed light signal that experiences a time delay difference, and it is located away from corresponding passage.According to the present invention, light assembled unit 125 is by sending to receiving element 165 to the part of signal, and remainder is sent to OSNR monitoring arrangement 100, and shunting is by the light signal of channel separation.

130 pairs of polarization adjustment units are changed by the polarization state of the light signal that Transmission Fibers 115 is received.

Polarization beam splitter 135 becomes mutually perpendicular first polarized component and second polarized component to the separate optical signals of being exported from polarization adjustment unit 130 by a feedback procedure.135 pairs first and second polarized components of polarization beam splitter are aimed at, so that they are parallel to two axles of polarization beam splitter 135.Therefore, polarization beam splitter 135 becomes corresponding PSP component to separate optical signals.

Feedback control unit 136 uses the signal of telecommunication spectrum control polarization adjustment unit 130 of second polarized component, makes first and second polarized components of light signal and two axles of polarization beam splitter 135 align.Polarization adjustment unit 130 is changed the polarization state of light signal according to the control signal of feedback control unit 136.

Feedback control unit 136 comprises optical detecting unit 140, filter cell 145, power detecting unit 150 and main control unit 155.Optical detecting unit 140 converts second polarized component of being exported from polarization beam splitter 135 to the signal of telecommunication.

Filter cell 145 is only by the part in 140 electrical signal converted of optical detecting unit, promptly only by that part in the predetermined frequency band.When data format was 10Gb/s NRZ (non-return-to-zero), filter cell carried out filtering to the center in the signal of telecommunication bandwidth of 10GHz frequency usually.Filter cell 145 uses the predetermined frequency band part of a band pass filter (BPF) by signal.

The size of the power of the signal of power detecting unit 150 145 filtering in detection filter device unit.The performance number that is detected is input to main control unit 155.Main control unit 155 is stored a previous measured performance number, and current measured performance number and previous measured performance number are compared.Main control unit 155 control polarization adjustment units 130 make current measured performance number less than previous measured performance number.

If feedback control unit 136 repeats feedback procedure, then as a result, performance number restrains on a minimum value.So, two PSP components are aligned to two axles of polarization beam splitter 135 parallel, and disconnected from each other, then, exported by two outgoing routes of polarization beam splitter 135.

In case two axles that the PSP component is aligned to polarization beam splitter 135 align, main control unit outputs to scrambler 110 to an operation start signal.

If receive the operation start signal from main control unit 155, then 110 pairs of the scramblers light signal that is input to Transmission Fibers 115 carries out scrambling.That is, scrambler 110 changes the light strength ratio between two PSP components, makes the power of a PSP component of exporting from an axle of polarization beam splitter 135 alternately have a maximum and a minimum value.

Maximum and the minimum value because of the light signal of the operation cycle property variation of scrambler 110 measured in luminous intensity measurement unit 160.Main control unit 155 calculates OSNR by using the maximum and the minimum value of the light signal of being measured by luminous intensity measurement unit 160, and it is exported.

Now, explain principle of separating two PSP components and the method for calculating OSNR in detail with reference to formula.

In Transmission Fibers 155, have fast axle and slow axis, that is, and two mutually perpendicular PSP.To represent two PSP by PSP+ and PSP-respectively.Suppose the light from monochromatic source to be incided Transmission Fibers 115 by an external modulator.The light of institute's incident has experienced differential group delay (DGD) τ between two PSP components _fA time delay poor, and conciliate multiplexed unit 120 by Transmission Fibers 115 and propagate, then by polarization adjustment unit 130 and polarization beam splitter 135, and be input to optical detecting unit 140.The power spectrum of opto-electronic conversion is carried out in 1 expression by optical detecting unit 140 as follows:

$S\left(\mathrm{\&omega;}\right)={\mathrm{\&alpha;}}_0^2{\mathrm{<figure-callout\; id="0"\; label="I"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">I</figure-callout>}}_0^2\{(a^4+{\mathrm{<figure-callout\; id="4"\; label="b"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">b</figure-callout>}}^4+2a^2{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">b</figure-callout>}}^2\cos \mathrm{\&omega;}{\mathrm{\&tau;}}_f){\left|F\left(\mathrm{\&omega;}\right)\right|}^2+4a^2{\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">b</figure-callout>}}^2{\left|H\left(\mathrm{\&omega;}\right)\right|}^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2{\mathrm{\&omega;}}_0{\mathrm{\&tau;}}_f$

$-4\mathrm{ab}\cos {\mathrm{\&omega;}}_0{\mathrm{\&tau;}}_f.\mathrm{Re}[a^2\exp \left(\mathrm{i\&omega;}{\mathrm{\&tau;}}_f\right)+b^2)F\left(\mathrm{\&omega;}\right)H^{*}\left(\mathrm{\&omega;}\right)\left]\right\}......\left(1\right)$

Herein, F (ω) and H (ω) represent cos respectively ²(Δ φ (t)/2) and cos (Δ φ (t+ τ)/2) cos (Δ φ (t)/2) and a=cos θ ₀Cos θ and b=sin θ ₀The Fourier transform of sin θ.Δ φ (t) (phasic difference of two waveguides of=π ([1-f (t)] f (t): data (0 or 1)) expression external modulator, ω ₀Expression signal light frequency, α ₀Expression comprises the loss of the overall optical link of light assembled unit 125, θ ₀Angle between expression optical fiber input polarisation of light and fast spool (PSP+), θ represents to be input to the angle between the polarization axle (x axle) of the light signal PSP+ component of polarization beam splitter 135 and polarization beam splitter 135.I ₀The luminous intensity of expression transmitting terminal light source, and be ω=2 π f.

Fig. 2 is expression simulation about the curve chart of the variable power of the major state (PSP) of polarization and the angle between the polarization beam splitter (PBS).When the data square pulse stream f (t) of any 10Gb/s NRZ light signal of hypothesis at-7T≤t≤7T (T: when bit period) being 01011100101100 in the time domain, then Fig. 2 is expression 10GHz band curve chart about the variable power of the angle between the axle of PSP and polarization beam splitter 135 when logical, and this obtains with analog form by changing filter width.Herein, θ ₀=π/6, τ _f=30 _Ps

Usually, the envelope of F (ω) of square pulse signal of PRBS pseudo-random bit sequence (PRBS) NRZ data with 1 bit period of T has a SIN function, and frequency f=n/T (n=1,2,3 ...) situation under value be 0.At this moment, show among Fig. 2: θ=n pi/2 (n=0,1,2 ...) time, S (ω) restrains on a minimum value.

When performance number restrains, promptly when θ be θ=n pi/2 (n=0,1,2 ...) in when one of any, two PSP components are paralleled, and disconnected from each other with two of polarization beam splitter 135 vertical axles.Be the Convergence Distributed Power value, feedback control unit is compared the current measured value of S (ω) and previous measured value, and a feedback voltage is provided in polarization adjustment unit 130, makes current measured value always less than previous measured value.

If repeat this feedback procedure, then performance number θ=n pi/2 (n=0,1,2 ...) convergence, thereby two PSP components that separated by polarization beam splitter 135 advance along different paths.

As shown in Figure 2, the variation for the band pass filter of filter cell 145 realizes this convergence equally.When filter width is big, the curve display of Fig. 2: θ=n pi/2 (n=2,4 ...) and θ=n pi/2 (n=1,3,5 ...) on different minimum values, restrain.Its reason is, the light intensity difference between two PSP and the finite filter bandwidth.

When data type is RZ (making zero) and pulse duration and when the bit time, ratio was 0.5, the monitoring frequency that can follow the tracks of PSP be f=2n/T (n=0,1,2 ...).Because this PSP tracking real-time operation, so even the PMD that changes on the time of occurrence, two PSP components also always separate, and keep this separation.

If two PSP components are separated on two axles of polarization beam splitter 135, and with they output, then main control unit 155 sends an order to the scrambler 110 that is positioned at hop, requires the optical fiber input polarization is carried out scrambling.Scrambler 110 changes the relative light intensity ratio of two PSP components, makes the power that repeats between a maximum and minimum value from a PSP component of an axle output of polarization beam splitter 135.At this moment, by following formula 2 expression maximum and minimum values:

Wherein, P _SAnd P _ASERepresent the power of light signal and the power of ASE noise respectively.According to this formula, can obtain OSNR, shown in following formula 3:

$\mathrm{OSNR}=\frac{P_S{B}_0}{P_{\mathrm{ASE}}{B}_r}=\frac{(P_{\max }-P_{\min }){\mathrm{<figure-callout\; id="0"\; label="B"\; filenames="A20041008268500181.png"\; state="\{\{state\}\}">B</figure-callout>}}_0}{2P_{\min }{B}_r}......\left(3\right)$

Wherein, B ₀The expression bandwidth of an optical fiber, B _rRepresent a predetermined resolution bandwidth.

Fig. 3 is the structure of an experimental provision, and this experimental provision is used for according to the present invention proving the structure and the principle of the device that is used for monitoring light signals experimentally.

With reference to Fig. 3, this experimental provision comprises laser diode 305～308,310, Mach-Zehnder of waveguide optical grating array (AWG) (mach-zehnder) intensity modulator 315, one first variable attenuator 317, PMD simulator 325, ASE source 335, one second variable attenuator 337, an optical spectrum analyser 340 and an OSNR monitoring arrangement 300.

To the 1555.7nm, the wavelength interval of the light source of exporting from each laser diode is 0.8nm to the optical wavelength of the light source of being exported from 4 laser diodes 305～308 at 1553.4nm.310 pairs of 4 passage light signals being exported from 4 laser diodes 305～308 of AWG carry out multipath conversion or separate multiplexedly, for this reason, have the channel spacing of 0.8nm and the passband of 0.41nm.

By an impulse waveform (pattenr) the mach-zehnder intensity modulator 315 that generator drove, generate one and have (2 ³¹-1) the 10Gb/s PRBS NRZ signal of waveform length.Being arranged on outside mach-zehnder intensity modulator 315 first variable attenuator 317 afterwards, is an external transducer, adjusts the signal light intensity.

PMD simulator 325 simulates the PMD in the present transmission optical link.The operating principle of PMD simulator 325 is: postpone separate and mutually perpendicular two polarised lights by polarization beam splitter on the time, and then they are combined in the polarization beam splitter.

ASE source 335 produces the ASE noise.ASE source 335 uses two image intensifers that formed by two gain elements to generate the ASE noise.Be arranged on ASE source 335 second variable attenuator 337 afterwards and change the ASE noise levels, to adjust OSNR.Optical spectrum analyser 340 is arranged on after PMD simulator 325 and the ASE source 335, with the spectrum of measuring light signal.According to measured spectrum, the performance of appraisal OSNR monitoring arrangement.With reference to the detailed analysis of explaining the ONSR performance of Fig. 4.

OSNR monitoring arrangement 300 comprises a polarization adjustment unit 345, linear polarizer 350, luminous intensity measurement unit 380, optical detecting unit 355, electric signal amplifier 360, a filter cell 365, power detecting unit 370, a main control unit 375 and a scrambler 320.Polarization adjustment unit 345, luminous intensity measurement unit 380, optical detecting unit 355, filter cell 365, power detecting unit 370, main control unit 375 and scrambler 320 are structurally illustrated in fig. 1 identical according to OSNR monitoring arrangement of the present invention 100 with above reference, with the detailed explanation of omitting them.

Use linear polarizer 350 to replace the polarization beam splitter 135 of the OSNR monitoring arrangement shown in Fig. 1.Light signal as a linear polarization of linear polarizer 350 outputs shows a polarization disappearance rate that is higher than the polarization disappearance rate (extinction ratio) of polarization beam splitter 135.

Optical coupler (not shown) is divided into two paths to the path for the output light of linear polarizer 350, has 1: 1 optical coupling rate.Along the light signal that one of this two paths advances, sequentially propagate along optical detecting unit 355, electric signal amplifier 360, filter cell 365 and power detecting unit 370, and arrive main control unit 375.Electric signal amplifier 370 has amplified a signal of telecommunication that is carried out opto-electronic conversion by optical detecting unit 355.

Main control unit sends a feedback control signal to polarization adjustment unit 345.Polarization adjustment unit 345 makes and has only one by linear polarizer 350 in two PSP components according to the polarization of this feedback control signal transmitting photo-signal.

If only a PSP component is by linear polarizer 350, then main control unit sends an operation start order to scrambler 320, and the maximum and the minimum value of order luminous intensity measurement unit 380 measuring light power.Then, main control unit 370 uses by luminous intensity measurement unit 380 measured maximum and minimum value, calculates OSNR.

Fig. 4 is the experimental provision by using Fig. 3 relatively the OSNR measurement error value and curve chart according to OSNR measurement error value of the present invention of prior art.

With reference to Fig. 4, when the PMD simulator is given as 10ps to DGD, the figure illustrates and have the OSNR measurement error value of the present invention of separating the PSP characteristic and do not have a comparative graph between the OSNR measurement error value that the output valve of linear polarizer of polarization adjustment unit of PSP separation process surveys by one of simple adjustment according to one.

Error amount among Fig. 4 shows when for all passages the input signal light intensity that is input to linear polarizer 350 being fixed on-10dBm, and when changing OSNR, measure the measurement value difference of value difference and optical spectrum analyser 340 according to the OSNR of these two kinds of methods by adjusting the ASE noisiness.

As shown in Figure 4, when DGD was 10ps, for all passages, the error amount that only uses polarization adjustment unit 345 and linear polarizer 350 to be surveyed was approximately 4.5～5.5dB, and when using tracking of the present invention and separating PSP, for the error amount of all passages less than about 0.4dB.

Fig. 5 is comparison for the OSNR measurement error value of the prior art of differential group delay and curve chart according to OSNR measurement error value of the present invention.

More particularly, when OSNR being fixed on about 25dB, separating PSP and use and separate under the situation of PSP, the variation that increase took place of the relative DGD of measurement OSNR measurement error value not using according to the present invention for passage 3 with 1554.9nm wavelength.Comparison to these results has been shown among Fig. 5.

As shown in Figure 5, when using according to optical signal monitor device of the present invention, although DGD increases, the OSNR measure error always is maintained a constant value in about 0.4dB scope, and in not using the experiment that separates PSP, the increase of the relative DGD of measure error and increasing.In addition, the relative increase curve of Fig. 5 demonstrates the tendency of big DGD value.

Fig. 6 is a flow chart of the performed step of the method that is used for monitoring light signals according to the present invention.

With reference to Fig. 6, in step S600,130 conversions of polarization adjustment unit are from the state of the polarization of a light signal of Transmission Fibers 115 inputs.

In step S605, polarization beam splitter 135 becomes mutually perpendicular first polarized component and second polarized component to the separate optical signals of wherein having changed polarized component.First and second polarized components that polarization beam splitter 135 is separated are separated, and they are outputed to luminous intensity measurement unit 160 and feedback control unit 136 respectively.Feedback control unit 136 control polarization adjustment units 130 make first and second polarized components be aligned to be parallel to two axles of polarization beam splitter.

If in step S610,, then carry out the following step if first and second polarized components that polarization beam splitter separated are not aligned to two axles that are parallel to polarization beam splitter.

In step S615, optical detecting unit 140 converts second polarized component to a signal of telecommunication, and in step S620, filter cell 145 only passes through a predetermined frequency band of this signal of telecommunication.In step S625, power detecting unit 150 is measured the power of the signal of telecommunication of institute's filtering.

In step S630, main control unit 155 is compared current measured power and previous measured power, to generate the signal of a control polarization adjustment unit 130, makes current measured power less than previous measured power.If receive control signal from main control unit 155, then in step S600,130 conversions of polarization adjustment unit are corresponding to the state and the direction of the polarized component of the light signal of this control signal.

If in step S610, first and second polarized components that polarization beam splitter 135 is separated are aligned to two axles that are parallel to polarization beam splitter 135, then carry out the following step.

In step S635, main control unit 155 sends to scrambler 110 to an operation start order.

In step S640, the 110 pairs of light signals of being exported from transmission unit 105 of scrambler that receive the operation start order carry out scrambling, and are entered into Transmission Fibers 115.Light signal through scrambling periodically repeats maximum and minimum value.

In step S645, the luminous intensity through first polarized component of the light signal of scrambling is measured in luminous intensity measurement unit 160.Because the light signal through scrambling periodically repeats maximum and minimum value, so maximum and minimum value are measured in luminous intensity measurement unit 160 in step S645.In step S650, main control unit 155 uses luminous intensity measurement unit 160 measured maximum and minimum value, calculates OSNR.

Below explained and shown preferred embodiment.Yet the present invention is not limited to these preferred embodiments described above.Obviously, the skilled artisan in the art can be in defined design of the present invention of claims and scope, becomes to change and revise these embodiment.

According to the present invention, change in of the variation of an ASE noise level, and on the transmission optical link, have in the WDM optical transmission system of PMD with passage, can accurately measure OSNR.In addition, even when PMD changes in time, also can accurately measure OSNR.

It is the priority of the korean patent application of 2003-75799 that the application requires the sequence number of application on October 29th, 2003, now its full content is incorporated into herein, with for referencial use.

Claims (12)

1. device that is used for monitoring light signals comprises:

A polarization adjustment unit is used to change a polarization state by the light signal that Transmission Fibers received;

A polarization beam splitter, it will become mutually perpendicular first polarized component and second polarized component from the separate optical signals that the polarization adjustment unit is exported;

A luminous intensity measurement unit is used to measure the luminous intensity of first polarized component;

A feedback control unit, it is by using the signal of telecommunication frequency spectrum of second polarized component, and control polarization adjustment unit is so that can make two axles of first and second polarized components and polarization beam splitter align; And

A scrambler, if feedback control unit aligns two axles of first and second polarized components and polarization beam splitter, then this scrambler carries out scrambling to the light signal that is input to Transmission Fibers.

2. device according to claim 1, wherein, the wherein luminous intensity of first polarized component of maximum and min periods variation is measured in the luminous intensity measurement unit.

3. device according to claim 1, wherein, feedback control unit comprises:

An optical detecting unit is exported the signal of telecommunication corresponding to second polarized component;

A filter cell, only a predetermined band signal by this signal of telecommunication;

A power detecting unit, the power of the signal that measurement is passed through;

A main control unit is compared current measured power and the previous measured power that power detecting unit detected, and the polarization adjustment unit is controlled, and makes current measured power less than previous measured power.

4. device according to claim 3, wherein, if two axles of first and second polarized components and polarization beam splitter align, then main control unit operation scrambler, an and luminous intensity calculating Optical Signal To Noise Ratio (OSNR) measured according to the luminous intensity measurement unit.

5. device according to claim 1, wherein, light signal is each passage in a wavelength division multiplexing (WDM) optical transmission system.

6. device according to claim 1 also comprises:

A wave length variable filter unit is arranged between Transmission Fibers and the polarization adjustment unit, and scans each wavelength channel from the wdm optical signal that Transmission Fibers received, but also each passage is outputed to the polarization adjustment unit.

7. method that is used for monitoring light signals comprises:

Conversion is by the state of the polarization of the light signal that Transmission Fibers received;

The separate optical signals that polarized component has wherein been changed becomes mutually perpendicular first polarized component and second polarized component;

Measure the luminous intensity of first polarized component;

By using the signal of telecommunication frequency spectrum of second polarized component, carry out FEEDBACK CONTROL, first and second polarized components and two axles being scheduled to are aligned; And

If by FEEDBACK CONTROL first and second polarized components and this two axles are aligned, then the light signal that is input to Transmission Fibers are carried out scrambling.

8. method according to claim 7 wherein, is measured and also to be comprised: measures the wherein luminous intensity of first polarized component of maximum and min periods variation.

9. method according to claim 7, wherein, FEEDBACK CONTROL comprises:

Export a signal of telecommunication corresponding to second polarized component;

Only pass through a predetermined band signal of this signal of telecommunication;

Measure the power of the signal of telecommunication that is passed through;

Measured power and previous measured power are compared, and control and make current measured power less than previous measured power;

10. method according to claim 9, control comprises:

If first and second polarized components and two axles are aligned, then the input signal to Transmission Fibers carries out scrambling, and calculates an Optical Signal To Noise Ratio (OSNR) according to measured luminous intensity.

11. method according to claim 7, wherein, light signal is each passage in a wavelength division multiplexing (WDM) optical transmission system.

12. method according to claim 7 also comprised before transition status and direction:

Scanning is from each wavelength channel of the wdm optical signal that Transmission Fibers received, but also each passage of output wdm optical signal.

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